The last two turning points have been described as a decrease in brain connectivity, which is believed to be linked to aging and the deterioration of the brain's white matter.
According to the British newspaper The Guardian, one of the most comprehensive studies to date on how neural connections change from childhood to old age has identified five key "phases" of human brain development.
The study, based on brain scans of nearly 4,000 people aged between one and 90, mapped neural connections and how they develop throughout our lives.
The study revealed five major phases, divided into four pivotal "turning points," at which brain organization shifts to a different trajectory, around ages 9, 32, 66, and 83.
"Looking back, many of us feel that our lives have been marked by distinct phases," says Professor Duncan Astle, a neuroinformatics researcher at the University of Cambridge and the study's lead author. "It turns out that brains also go through these phases."
Understanding that the brain’s structural journey is not a matter of steady evolution, but rather one of a few major turning points, will help us determine when and how its neural networks are susceptible to disruption.
The childhood period of development is found to occur from birth to age nine, after which it transitions into adolescence, a phase that lasts until an average age of 32.
In a person’s early thirties, the brain’s neural networks transition into adulthood, the longest phase, lasting more than three decades. The third turning point begins around age 66 and marks the beginning of “premature aging” in brain structure. Finally, the brain reaches its full maturity around age 83.
Measuring Brain Organization
Scientists have measured brain organization using 12 different metrics, including the efficiency of neural connections, their fragmentation, and whether the brain is highly centralized or has a more diffuse network.
From infancy to childhood, our brains are known as “network consolidation,” where the number of synapses—the connections between neurons—decreases in the infant brain, while the most active cells remain. During this period, the study found that the efficiency of brain connections decreases.
Meanwhile, the volume of gray and white matter grows rapidly, with cortical thickness—the distance between the outer gray matter and the inner white matter—reaching its peak, and cortical folding, the characteristic ridges of the outer brain, stabilizing.
In the brain’s second “age,” adolescence, white matter continues to grow, leading to a significant improvement in the organization of the brain’s communication networks. This era is characterized by a steady increase in the efficiency of neural connections throughout the brain, which is associated with enhanced cognitive performance. These periods are defined by the brain remaining on a stable growth trajectory over a long period, rather than remaining in a static state all the time. “We certainly don’t mean that people in their late twenties will behave like teenagers, or even that their brains look like teenagers’ brains,” says Alexa Mosley, who led the research. “It’s really the pattern of change.”
She added that the findings could offer insights into the risk factors for mental health disorders, which often emerge during adolescence. Around age 32, the most significant overall shift in the brain's trajectory is observed. Life events, such as parenthood, may play a role in some of the noticeable changes, although research hasn't explicitly tested this.
"We know that the brains of women who give birth change after childbirth," Mosley said. "It's reasonable to assume there's a connection between these milestones and what's happening in the brain." Beginning around age 32, brain structure appears to stabilize compared to earlier stages, consistent with "stabilization of intelligence and personality" based on other studies. Brain regions also become more compartmentalized.
These final two turning points have been described as a decrease in brain connectivity, which is thought to be linked to aging and the deterioration of the brain's white matter.